Through-dyeing of cotton warp yarns with indigo

ABSTRACT

The present invention relates to a process for through-dyeing of cotton warp yarns with indigo in an indigo dyeing range, which comprises dyeing in one pass at a dyeing temperature of 30 to 90° C. and an indigo concentration of 10-60 g/l.

The present invention concerns a process for through-dyeing of cotton warp yarns with indigo and also textile articles comprising thus dyed cotton warp yarns.

Denim refers to a relatively coarse woven cotton fabric which was originally used for robust workwear, but today is used particularly for manufacturing fashionable jeans articles. The warp yarns needed to produce denim can be dyed with indigo or else with sulfur dyes, especially sulfur black, although dyeing to blue with indigo is greatly predominant.

Traditionally, the warp yarn is dyed with indigo as a rope or as a warp yarn sheet on specific dyeing ranges which consist of a combination of one or more troughs with squeeze rolls and a subsequent skying sector. The reduced dye is applied in the troughs and oxidized in the skying sector (see for example Technical Information TI/T 017 from BASF AG dated June 1995, title: Continuous dyeing with indigo). The dyeing is typically carried out in a dyebath at room temperature or slightly elevated temperatures of about 20-35° C., a pH of about 10.5 to 14 and an indigo concentration of about 0.5 to 10 g/l. Wetting agents in a concentration of about 0.1 to 5 g/l can be used as well. A redox potential in the dyebath is maintained by using an excess of hydrosulfite reducing agent in amounts of about 0.1 to 5 g/l. The yarn contact time with the dyebath is generally 8 to 30 seconds per pass. Dyeing in multiple passes, i.e., the repeated application of dye from the dyebath by dipping with subsequent squeezeoff in the dyeing trough and the following skying, makes it possible to achieve deeper shades (see for example ITB Veredlung 2/90, title: Indigo-Färberei: Verfahrens-und maschinentechnische Lösungen, author: Dipl. Ing. L. Haas).

German Patent Application DE 196 29 985 describes single-pass dyeing wherein, to overcome the low affinity of indigo, the dyebath additionally has added to it salt in the form of sodium chloride in order that an electrolyte concentration of 200 to 350 g/l may be set.

These processes all produce a so-called ring dyeing, i.e., the fiber is dyed at the surface only, leaving the interior of the fiber, the core, undyed. Ring dyeing makes it possible to endow made-up denim articles with a high-contrast appearance in particular washing and/or bleaching processes through a wash-down of the initially dark blue fabric. An example is the familiar stone-wash effect, which is achieved by washing the made-up article with enzymes and pumice stones.

However, there are already signs that future jeans fashion will demand effects which cannot be achieved with ring-dyed denim alone. On the contrary, core-dyed warp yarns have to be available for the development of new articles if these demands are to be met.

The dyeing processes required have to be economical in that they should not require additional cost and inconvenience on the part of the dyer, but should be simple to carry out, ideally in a dyer's existing dyeing equipment.

The present invention, then, provides such a process.

The invention relates to a process for through-dyeing of cotton warp yarns with indigo in an indigo dyeing range, which comprises dyeing in one pass at a dyeing temperature of 30 to 90° C. and an indigo concentration of 5-500 g/l.

An indigo dyeing range in the realm of the present invention is a range which consists of one dyeing trough or a combination of multiple dyeing troughs with squeeze rolls and subsequent skying sectors (see for example ITB Veredlung 2/90, title: Indigo-Färberei: Verfahrens-und maschinentechnische Lösungen, author: Dipl. Ing. L. Haas).

Any commercially available indigo may be used. Indigo is preferably used in amounts of 5-500 g/l and more preferably in amounts of 10 to 50 g/l.

It is particularly advantageous to use pre-reduced indigo to carry out the process of the invention. The pre-reduced indigo used is ideally produced from indigo without use of reducing agent, such as sodium dithionite for example, but by catalytic hydrogenation. It is most advantageous to use indigo in the form of a leuco indigo solution as described for example in EP 1 097 184 B1 and offered on the market by DyStar Textilfarben GmbH & Co. Deutschland KG.

To stabilize leuco indigo, i.e., to back-reduce leuco indigo which has become oxidized in the dyebath, it is preferable to use a hydrosulfite excess of 0.1 to 5 g/l and more preferably 0.2 to 2 g/l. It will be appreciated that in lieu of the hydrosulfite it is possible to use other suitable reducing agents, for example glucose or hydroxyacetone, or else combinations of various reducing agents such as glucose/hydrosulfite.

The temperature at which the process of the invention is carried out is preferably 30-90° C. and more preferably in the range from 50 to 70° C.

The process of the invention can be carried out with or without wetting agent, but preferably it is carried out in the presence of a wetting agent. Examples of suitable wetting agents are anionic wetting agents, for example fatty alcohol ethoxylate, alkanesulfonate, sulfosuccinate, alkyl phosphate or paraffins and hydrocarbons or else mixtures thereof, and most preference is given to using salts of phosphoric esters.

The amounts in which the wetting agents mentioned are used are preferably in the range from 5 to 50 g/l and more preferably in the range from 10 to 25 g/l.

Dyebath pH in the process of the invention is preferably in the range from 10.5 to 13.5.

The process of the invention surprisingly leads in just one pass to yarns which are through-dyed, i.e., dyed in the core as well in the surface region. The contact time with the dyebath is preferably 8 to 30 seconds and more preferably 15 to 20 seconds. The subsequent skying takes preferably 90 to 130 seconds and more preferably 100 to 1 10 seconds.

It is a particular advantage to the dyer that the process of the invention ends after just one pass. This is because this leaves the dyer with the option of using the other dyeing troughs of his indigo dyeing range which are not needed for dyeing to subject the dyed cotton warp yarn to further treatment steps. Alternatively, the dyer also has the option of course of realizing more economical, small-scale ranges.

The process of the invention is particularly surprising because the properties of indigo did not suggest that the use of high indigo levels leads to a satisfactory dyed result. On the contrary, it had hitherto been assumed that the large indigo dyeing ranges of the prior art are indispensable for this purpose.

The core-dyed cotton warp yarns dyed in the core by the process of the invention can be subjected to further treatment steps to obtain certain effects and then be conventionally woven up and processed into textile articles for the consumer, such as garments in particular.

However, it is also possible for the dyed cotton warp yarns to be processed into textile articles without further treatment and, if desired, only then to undertake further treatment steps, i.e., to modify the already made-up merchandise.

It is of course similarly possible to subject not only the dyed cotton warp yarns but also the textile articles produced therefrom to further processing steps.

The cotton warp yarns dyed by the process of the invention can of course also be woven up, and further processed into articles for the consumer, in admixture with further materials. Blends with elastane may be mentioned by way of example.

The present invention also provides textile articles comprising cotton warp yarns dyed by the process of the invention. Examples of such textile articles are denim fabrics which have not been made up, but in particular garments such as pants, skirts, shirts, jackets, etc. or other textile type articles.

The examples which follow illustrate the invention. The parts in the table examples are by weight.

EXAMPLE 1

A commercially available unpretreated dry cotton warp yarn was dyed from a dyeing liquor of the following composition:

-   -   20 g/l of indigo as commercially available DyStar Indigo Vat 40%         solution     -   2 g/l of hydrosulfite (BASF Hydrosulfit konz.)     -   20 g/l of wetting agent (Primasol NF)

The pH of the liquor was 13.

The yarn was dyed at 50° C. in the course of a dip time of 25 seconds. The subsequent skying took 120 seconds.

This was followed by two rinses with water at 20° C.

A through-dyed yarn having a high level of applied indigo was obtained. A dye analysis of the dyed yarn revealed a level of 5.8%.

EXAMPLE 2

A commercially available unpretreated dry cotton warp yarn (yarn count: 8.5 Ne, 24 per rope) was dyed from a dyeing liquor of the following composition:

-   -   25 g/l of indigo as commercially available DyStar Indigo Vat 40%         solution     -   5 g/l of hydrosulfite (BASF Hydrosulfit konz.)     -   25 g/l of wetting agent (Primasol NF)

The pH of the liquor was 12.6.

The yarn was dyed at 60° C. in the course of a dip time of 10 seconds. The subsequent skying took 120 seconds. The yarn throughput was 12.61 kg/min.

This was followed by two rinses with water at 20° C.

A through-dyed yarn having a high level of applied indigo was obtained. A dye analysis of the dyed yarn revealed a level of 6%.

The table examples which follow describe further embodiments of the process of the invention. They are carried out similarly to the abovementioned examples 1 and 2. A through-dyed yarn having a high level of applied indigo is obtained in each case. Product Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 DyStar Indigo Vat 100 450 200 120 40% solution DyStar Indigo Vat 35 60% grains DyStar Indigo granules 80 Hydrosulfite conc. (BASF) 5 70 1 10 Glucose 10 20 20 2 Fatty alcohol ethoxylate 10 and alkanesulfonate Sulfosuccinate Paraffins, hydrocarbons 30 and fatty alcohol ethoxylate Alkyl phosphate 20 20 10 Fatty alcohol ethoxylate and alkyl phosphates pH 13 11.8 12.8 13 12.4 11.0 Temperature (° C.) 50 80 90 70 50 70 Number of passes 1 1 1 1 1 1 

1. A process for through-dyeing of cotton warp yarns with indigo in an indigo dyeing range, which comprises dyeing in one pass at a dyeing temperature of 30 to 90° C. and an indigo concentration of 5-500 g/l.
 2. A process according to claim 1 that utilizes indigo in the form of a solution of leuco indigo.
 3. A process according to claim 2 wherein the leuco indigo has been produced from indigo by catalytic hydrogenation.
 4. A process according to claim 1 wherein the process is further carried out in the presence of a wetting agent.
 5. A process according to claim 4 wherein the wetting agent is used in amounts of 5 to 50 g/l.
 6. A textile article comprising cotton warp yarns dyed by the process according to claim
 1. 7. A process according to claim 3, wherein the process is further carried out in the presence of a wetting agent.
 8. A process according to claim 7, wherein the wetting agent is used in amounts of 10 to 25 g/l.
 9. A process according to claim 1, wherein said indigo concentration is 10-50 g/l.
 10. A process according to claim 1, wherein said indigo is a pre-reduced indigo.
 11. A process according to claim 10, wherein the pre-reduced indigo is produced from an indigo without the use of a reducing agent.
 12. A process according to claim 2, wherein the temperature is from 50 to 70° C.
 13. A process according to claim 1, wherein the dyeing is conducted at a pH from 10.5 to 13.5.
 14. A process according to claim 8, wherein the wetting agent is fatty alcohol ethoxylate, alkanesulfonate, sulfonsuccinate, alkyl phosphate, paraffin, hydrocarbon or mixtures thereof.
 15. A process according to claim 8, wherein the wetting agent is a salt of phosphoric esters. 